The present invention relates to new metal complexes of halogen-substituted o-benzenedithiols, new halogen-substituted o-benzenedithiols used as starting materials therefor, processes for producing the same and plastic compositions containing said metal complexes as near-infrared absorbers.
Known o-benzenedithiols such as benzene-1,2-dithiol, 1-methylbenzene-3,4-dithiol, 1,2-dimethylbenzene-4,5-dithiol and 1,2,3,4-tetramethylbenzene-5,6-dithiol have a high metal chelating capacity. It has been known that metal complexes of o-benzenedithiols obtained by reacting the thiols with metal ions, such as bis(1,2-dithiophenolato) nickel-tetra-n-butylammonium, bis(1-methyl-3,4-dithiophenolato)nickel-tetra-n-butylammonium, bis (1,2,3,4-tetramethyl-5,6-dithiophenolato)nickel-tetra-n-butylammonium and bis(1,2,3,4-tetrachloro-5,6-dithiophenolato)nickel-tetra-n-butylammonium exhibit a specific absorption spectrum in a near-infrared zone ["Toluol-3,4-dithiol und verwandte 1,2-Dithiolene als Chelatbildner for Metalle" Monatschefte fur Chemie, Vol. 102, pp. 308-320 (1971) and "Characterization and Electronic Structures of Metal Complexes Containing Benzene-1,2-dithiolate and Related Ligands" Journal of the American Chemical Society, Vol. 88, pp. 4870-4875 (1966)]. These metal complexes having excellent thermal stability and weather resistance (Japanese Patent Laid-Open No. 135551/1981) are used as important near-infrared absorbers. Investigations are made on the use of them by incorporating them as near-infrared absorbers in plastic films or plates or by applying polymer solutions containing them to bases to form films for agricultural use for the selective absorption of the sunlight as well as sunglasses, welder's glasses, aircraft windows and TV filters so as to reduce the glare of the light or fatigue of eyeballs. Further, recently, investigations are made of the use of the metal complexes for producing optical filters for the compensation of wavelength dependence of the sensitivity of optical transducer elements such as photodiodes and light-emitting diodes. These metal complexes are used also as important absorbers and regenerators of laser beams for semiconductor laser beam recording, i.e. laser heat mode recording, since the near-infrared absorption zone of them coincides with the oscillation wavelength of the semiconductor lasers.
However, known metal complexes of o-benzenedithiols excluding those derived from 1,2,3,4-tetrachlorobenzene-5,6-dithiol (Japanese Patent Laid-Open No. 135463/1981) are quite expensive, since they are produced by complicated, multi-step synthesis reactions. Therefore, the uses of them have been limited.
On the contrary, since the above-mentioned tetrachlorobenzenedithiol can be produced economically advantageously and a metal complex derived therefrom has an excellent near-infrared absorbing capacity, this complex has been used practically. However, if resins in the form of films or plates containing a large amount of this complex as near-infrared absorber are used, the metal complex of tetrachlorobenzenedithiol is crystallized out of the resin. For example, if 20 wt. % or more of the metal complex is incorporated in an acrylic resin, this phenomenon occurs particularly remarkably. Therefore, this complex is unsuitable if it should be contained in a high concentration in a resin, particularly when a high near-infrared absorbing capacity is required of a thin film containing a high concentration of the complex prepared according to a coating method.